1. Field of the Invention
The present invention relates to a piezoelectric transformer which converts a primary voltage to a secondary voltage by utilizing a deformation of a piezoelectric element during a supply of a voltage. Particularly, the present invention relates to a high output stacked type piezoelectric transformer in which the capacitance values of input and output are increased to realize a high output, and to lower the heat release temperature.
2. Description of the Prior Art
Generally, the basic principle of the piezoelectric transformer is as follows. That is, if a voltage is impressed on a part of the body of a piezoelectric element, then, a deformation occurs on the part, and then, the deformation propagates to other parts. This phenomenon is utilized in the piezoelectric transformer. This piezoelectric transformer is classified into various kinds depending on the shapes and oscillation modes of the input and output sides. Among them, a ring-dot type piezoelectric transformer which is considered as a ballast piezoelectric transformer is illustrated in FIGS 1a and 1b. 
FIG. 1a is a plan view of the conventional ring-dot type piezoelectric transformer. FIG. 1b is a sectional view of the conventional ring-dot type piezoelectric transformer. As shown in FIG. 1a, the ring-dot type piezoelectric transformer is divided into a ring region and a dot region by an annular open region OP. Referring to FIG. 1b, the ring-dot type piezoelectric transformer includes: a piezoelectric element 11; an input electrode INE formed on the top of the piezoelectric element 11, for being connected to an input terminal IN, the input terminal IN receiving a primary voltage; an output electrode OUTE electrically isolated from the input electrode INE by the open region OP, and connected to an output terminal OUT, the output terminal OUT receiving a secondary voltage; and a ground electrode GE formed on the bottom of the piezoelectric element 11 and connected to the ground. In the above, the dot portion may become the input electrode INE, and the ring portion may become the output electrode OUTE. On the other hand, the ring portion may become the input electrode INE, and the dot portion may become the output electrode OUTE.
In the conventional ring-dot type piezoelectric transformer, if an input voltage of the resonance frequency is supplied to the input electrode INE of FIG. 1b, i.e., to the dot of FIG. 1a, then contraction-expansion oscillations occur in the planar direction of FIG. 1b (in the direction of the arrow mark). Under this condition, contractions-expansions occur in the thickness direction in the opposite manner, with the result that the output electrode OUTE outputs a voltage owing to the piezoelectric effect.
However, in the conventional ring-dot type piezoelectric transformer, the capacitances of the input and output sides are very small, and therefore, it is not suitable for using it as a high output transformer. Even if it is used as a high output transformer, if the oscillation speed increase above a certain level, then the heat release temperature is steeply raised, with the result that the transformer departs from the allowance value.
The present invention is intended to overcome the above described disadvantages of the conventional technique.
Therefore it is an object of the present invention to provide a high output stacked type piezoelectric transformer in which the capacitance values of input and output are increased to realize a high output, and to lower the heat release temperature.
In achieving the above object, the high output stacked piezoelectric transformer according to the present invention includes: a first piezoelectric element; a first input electrode formed upon the first piezoelectric element; a first output electrode electrically isolated from the first input electrode; a ground electrode formed on the bottom of the first piezoelectric element; a second piezoelectric element formed under the ground electrode; a second input electrode formed on the bottom of the second piezoelectric element; and a second output electrode electrically isolated from the second input electrode.